Raymond J.G. Leakey

Picoplanktonic community structure on an Atlantic transect from 50°N to 50°S

Plankton samples were collected from 10 depths at 25 stations spaced at intervals of about 4° of latitude along a transect from the British Isles to the Falkland Islands. Four categories of picoplankton were discriminated: Synechococcus spp., Prochlorococcus spp., eukaryotic picophytoplankton and heterotrophic bacteria. The populations in each category in the samples were counted by flow cytometry and the mean size of bacterial cells was determined by fractionation through filters. Categories of phototrophic cells were discriminated by size and by the fluorescence of photosynthetic pigments; samples stained with the fluorochrome TOTO were used to enumerate heterotrophic bacteria (and Prochlorococcus in surface waters where their chlorophyll content was very small). The carbon biomass concentration of each category in each sample was calculated. Prochlorococcus was present at all stations between 47°N and 38°S, and reached peak population densities above 200,000 cells ml-1 in equatorial waters; the depth occupied by these cells increased in oligotrophic waters, where they dominated picophytoplankton biomass. Synechococcus reached high concentrations in the Mauritanian upwelling region and in the frontal region near the southern end of the transect, where they represented the largest single component of picophytoplankton biomass, but was almost absent in oligotrophic regions. Picoeukaryotes were present in low numbers at all latitudes, but they are larger cells and constituted a substantial part of the total picophytoplankton biomass at most latitudes. The depth-integrated (200 m) biomass of heterotrophic bacteria was nearly as great as that of the picophytoplankton at all latitudes, because substantial numbers of cells occurred at all depths. Numbers and biomass of these bacteria were maximal in the upwelling region and high at both ends of the transect. There was a clear contrast in the composition of the picoplankton community in both the North and South Atlantic between mesotrophic waters where Synechococcus and picoeukaryotes dominated the biomass, and oligotrophic waters where the smaller total biomass was dominated by Prochlorococcus.

Picoplankton community structure on the Atlantic Meridional Transect: a comparison between seasons

Abstract Samples collected from 10 depths at 25 stations in September–October 1996 and 12 depths at 28 stations in April–May 1997 on an Atlantic Meridional Transect between the British Isles and the Falkland Islands were analysed by flow cytometry to determine the numbers and biomass of four categories of picoplankton: Prochlorococcus spp, Synechococcus spp, picoeukaryotic phytoplankton and heterotrophic bacteria. The composition of the picoplankton communities confirmed earlier findings ( Zubkov, Sleigh, Tarran, Burkill & Leakey, 1998 ) about distinctive regions along the transect and indicated that the stations should be grouped into five provinces: northern temperate, northern Atlantic gyre, equatorial, southern Atlantic gyre and southern temperate, with an intrusion of upwelling water off the coast of Mauritania between the northern Atlantic gyre and equatorial waters. Prochlorococcus was the most numerous phototrophic organism in waters of both northern and southern gyres and in the equatorial region, at concentrations in excess of 0.1×106ml−1; it also dominated plant biomass in the gyres, but the biomass of the larger picoeukaryotic algae equalled that of Prochlorococcus in the equatorial region; higher standing stocks of both Prochlorococcus and picoeukaryotes were present in spring than in autumn in waters of both gyres. In temperate waters at both ends of the transect the numbers and biomass of picoeukaryotes and, more locally, of Synechococcus increased, and the Synechococcus, particularly, were more numerous in spring than in autumn. There was a pronounced southward shift of the main populations of both Synechococcus and Prochlorococcus in April–May in comparison to those of September–October, associated with seasonal changes in solar radiation, the abundance of Prochlorococcus dropping sharply near the 17°C contour, while Synechococcus was still present at temperatures below 10°C. Picoeukaryotes were more tolerant of low temperatures and lower light levels, often being more abundant in samples from greater depths, where they contributed to the deep chlorophyll maximum. Heterotrophic bacterial numbers and biomass tended to be highest in those samples where phototrophic biomass was greatest, with peaks in temperate and equatorial waters, which were shifted southwards in April–May compared with September–October.

Effects of temperature and nutrient regimes on biomass and lipid production by six oleaginous microalgae in batch culture employing a two-phase cultivation strategy

Commercial success of algal-based biofuels depends on growth characteristics and lipid metabolism of the production species. The oleaginous microalgae, Thalassiosira pseudonana, Odontella aurita, Nannochloropsis oculata, Isochrysis galbana, Chromulina ochromonoides, and Dunaliella tertiolecta, were cultivated under a matrix of two temperatures (10 and 20 °C) and two nutrient regimes (deplete and replete). For all species, a strong negative correlation between growth rate and lipid content was observed. Multiple stressors have no additive effect on lipid accumulation. Total oil content (fatty acid methyl esters, FAMEs, pg cell(-1)) was increased more by nutrient limitation than by temperature stress. In response to nutrient stress, N. oculata emerged as the most robust species with an increase in lipid accumulation of up to three to four-fold compared to the accumulation under nutrient sufficient conditions. Although stress conditions led to reduced fatty acid unsaturation in most taxa due to increased triacylglycerol (TAG) production, a high proportion of eicosapentaenoic acid (EPA) was maintained in O. aurita.

Synechococcus And Its Importance To The Microbial Foodweb Of The Northwestern Indian-Ocean

Abstract The abundance, distribution, size, biomass, growth and grazing-induced mortality of phycoerythrin (PE) rich chrococcoid cyanobacteria were studied during September-October 1986 in the Arabian Sea, the Gulf of Oman and the monsoonal upwelling region off the South East Arabian coast. Cyanobacteria were abundant (>107 cells 1−1) through the region and particularly so (>108 cells 1−1) in oligotrophic waters where they exhbited distinct subsurface concentration maxima that were situated above, but related to the depth of the chlorophyll maxima. Cell diameter increased from 0.7 μm in surface waters to 1.2 μm at depth. Standing stocks of cyanobacteria ranged up to 50μgC 1−1, and accounted for up to 40% of the POC in oligotrophic stations indicating that Synechococcus constitutes an important trophic resource. Experimental investigations showed that cyanobacterial populations were growing fast, with specific growth rates of 0.5–1.0 day−1, while simultaneously experiencing high mortality due to microzooplankton grazing. Grazing rates varied between 0.3 and 1.2 day−1, indicating that 31–71% of the cyanobacteria were predated daily. Grazing and cyanobacterial growth were correlated, suggesting that Synechococcus production and its fate by microbial grazing activity were tightly coupled. Cyanobacteria are clearly a major component of a dynamic but well-balanced microbial foodweb present in oligotrophic regions of the northwest Indian Ocean.

SALINITY-TEMPERATURE TOLERANCE AND OSMOREGULATION IN EURYTEMORA-AFFINIS (POPPE) (COPEPODA, CALANOIDA) IN RELATION TO ITS DISTRIBUTION IN THE ZOOPLANKTON OF THE UPPER REACHES OF THE FORTH ESTUARY

Abstract Eurytemora affinis (Poppe) was the dominant copepod in summer and winter surveys of the littoral zooplankton of the upper Forth estuary, Scotland. Maximum numbers were observed in the 0–10%. segment, reaching 500000· m −3 in summer and consistently exceeding main channel abundances reported from other studies. In winter, E. affinis was less abundant, and shared dominance with the rotifer Synchaeta , which occasionally reached numbers of 311000·m −3 . Tidal movements and seasonal changes in freshwater flow were both observed to effect longitudinal displacement of plankton populations. Laboratory tests of salinity-temperature tolerance in Eurytemora showed optimal conditions to be 3–10%. at low temperatures, broadly matching distribution patterns in the estuary. Salinity acclimation tests and haemolymph concentration measurements showed that copepods could adapt to changing conditions within 12 h (i.e. the duration of a tidal cycle). Acclimation extended tolerance limits in the direction of the acclimation treatment, with survival being enhanced by gradual rather than abrupt changes in salinity. Investigation of haemolymph Δ°C in a range of test salinities revealed a pattern of hyper/hypo-osmoregulation, with concentrations hyperosmotic to the external medium below 15%. and evidence of hypo-osmoregulation at salinities >20%.. Minimum haemolymph concentrations were found to be equivalent to ≈6%. sea water (Δ°C = 0.4) when held in fresh water. No evidence of salinity-associated respiratory distress was found in respiration experiments. The oxygen consumption values determined (5–7.5 μl O 2 ·mg dry wt −1 ·h −1 ) at optimal salinities and temperatures were similar to reported values for copepods of comparable size.

Planktonic ciliates in Southampton Water: abundance, biomass, production, and role in pelagic carbon flow

The abundance and biomass of marine planktonic ciliates were determined at monthly intervals at two stations in Southampton Water between June 1986 and June 1987. The two stations, an outer one at Calshot and an inner one at N. W. Netley, were subject to differing marine and terrestrial influences. The potential ciliate production at cach station on each visit was estimated from these data. Enumeration of ciliates and measurements of biovolume were performed on Lugols iodinepreserved samples and potential production was calculated using a predictive relationship based on temperature and cell volume. Heterotrophic ciliate abundance and biomass were greatest at both stations during spring and summer months, with respective maxima of 16x103 organisms 1-1 and 219 μg Cl-1 recorded at N. W. Netley. Estimates of the potential production of the ciliate community ranged from <1 to 18 μg Cl-1 d-1 at Calshot and <1 to 141 μg Cl-1 at N. W. Netley, with annual values of 2 and 9 mg Cl-1 yr-1, respectively. Abundances, biomass and potential production estimates were generally greater at N. W. Netley than at Calshot. Carbon flow through the ciliate community was assessed using annual production values from both this study and the literature. The annual ciliate carbon requirement was equivalent to 9 and 11% of annual primary production at Calshot and N. W. Netley, and potential annual ciliate production was equivalent to 34% and >100% of the energy requirements of metazoan zooplankton at these locations, although comprising only 8 and 10% of their available food.

Invertebrates in the litter and soil at a range of altitudes on Gunung Silam, a small ultrabasic mountain in Sabah

The numbers and biomass of litter and soil invertebrate fauna were investigated in six plots at altitudes of 280 m, 330 m, 480 m, 610 m, 790 m and 870 m on Gunung Silam, Sabah, East Malaysia. There were relatively high numbers and biomass in the lower plots, where the Oligochaeta were a high proportion of the total invertebrate biomass. The biomass of other invertebrate groups was low in the soil. There was a marked effect of altitude, particularly for the Oligochaeta above 610 m. The low biomass of the Oligochaeta in the higher plots suggested that the importance of this group may be diminished at relatively low altitudes on small mountains. However, several other soil faunal groups showed no evidence of an altitudinal effect, and it is suggested that the stunted forests near the summits of small mountains such as Gunung Silam may have a different litter and soil fauna from forests of a similar physiognomy at high elevations on large mountains.

Planktonic Ciliates In Southampton Water - Quantitative Taxonomic Studies

The species-specific abundance and biomass of marine planktonic ciliates were determined at monthly intervals at two stations in Southampton Water between June 1986 and June 1987. The two stations, an outer one at Calshot and an inner one at north-west Netley, were subject to differing marine and terrestrial influences. A total of 55 ciliate taxa were recorded during the sampling period; of these 34 taxa were identified to genus and 16 to species. The heterotrophic ciliate community at both stations was dominated by aloricate taxa which comprised >90% of the community abundance and biomass during some months. The loricate tintinnids were also common, especially at Calshot, during winter months. Oligotrichs dominated the aloricate community at both stations with haptorids prominent at north-west Netley. At Calshot, Strotnbidium sp. dominated the heterotrophic community abundance and biomass throughout the study period, while Askenasia sp., Strobilidium sp. and Tintinnopsis sp. were also common. Strombidium sp. also contributed most to heterotrophic community abundance at north-west Netley. Balanion sp. and Tintinnopsis sp. were also abundant. However, Cydotrichium sp. and Didiniunt sp. dominated community biomass at this station. Most taxa exhibited a seasonal cycle with low winter and high spring and summer abundances. Some taxa reached abundances of >2000 l 1 However, maximum abundance of one species of Tintinnopsis was found during winter months. The autotrophic ciliate, Mesodinium rubrum , was also recorded at both stations achieving densities >10 5 l 1 at north-west Netley during ‘bloom’ conditions.

Ciliate growth rates from Plymouth Sound: comparison of direct and indirect estimates

1. Observations are given on the vertical distribution of Sagitta elegans and S. setosa in the daytime. 2. An account is given of the seasonal abundance of both species of Sagitta throughout the year as shown by collections made with oblique hauls with the 2-metre stramin ring-trawl and hauls with a bottom plankton net. 3. An attempt is made to piece together as much as possible of the life-stories and habits of Sagitta in offshore waters off Plymouth on the basis of these and previous observations.

The abundance and biomass of choanoflagellates and other nanoflagellates in waters of contrasting temperature to the north-west of South Georgia in the Southern Ocean

The abundance and biomass of different categories of autotrophic and heterotrophic nanoflagellates were determined in surface waters along a transect crossing the Polar Front to the north-west of South Georgia in the Southern Ocean during the austral summer 1996. In the nanoflagellate community 14 choanoflagellate species and 11 other taxonomic categories were recognised. Total nanoflagellate abundance and biomass during the study varied from 4–56 × 10 5 litre –1 and from 3–20 μg C litre –1 respectively, with highest abundance and biomass of both autotrophic and heterotrophic nanoflagellates recorded in surface waters to the north of the Polar Front. The most common choanoflagellates were Bicosta spinifera , Calliacantha spp., Diaphanoeca pedicellata and Parvicorbicula socialis . Of these Calliacantha spp. dominated warmer waters north of the Polar Front with B. spinifera dominating colder waters to the south. Positive relationships between several nanoflagellate categories and temperature were identified but no relationships were found with either chlorophyll a or bacterial biomass. Overall the study has revealed significant differences in the abundance, biomass and quantitative importance of different taxonomic categories of nanoflagellates in offshore waters of differing physico-chemical character north and south of the Polar Front. However, the factors responsible for the distribution of nanoflagellates remain unresolved.